The producers of The Krusty Show want to change the format of the show in order to appeal to a wider audience (specifically young girls). They force Krusty to hire a female co-star. If he doesn't agree then they will fire him and hire a replacement via a new Fox reality show, America's Next Krusty.
The next day, Krusty introduces his new co-star, Princess Penelope (voiced by Anne Hathaway), who comes out singing a sappy "little girl in love" song for her debut, turning Krusty's show into something completely girly, clichÃ© and wishy-washy - with unicorns, rainbows, etc.
The new format changes the feel of the show and drives the boys away. Krusty's audience is now all girls and all they want to see is Princess Penelope and her unicorn. Krusty thinks that the new format will ultimately hurt the show and is completely against the new arrangement.
Bart (like all of the other boys) is unhappy with the new show. Bart goes into "Krustylu Studio Store, the Krusty-est Store on Earth" and finds only Princess Penelope merchandise. All the Krusty merchandise is out in the alley in the dumpster. Bart finds Krusty sitting next to the dumpster (eating gin sandwiches) and encourages Krusty to get a grip on reality and take control.
Krusty bursts into Princess Penelope's dressing room to take his show back, but then she confesses to him that she loves him and has loved him since she was 12. The next day on The Krusty and Princess Penelope "Smoochie Poo - I Love You Hour," Krusty declares his love for Penelope. Bart is upset and unplugs the TV.
Each day gets worse on The Krusty Show for Bart and the boys. Krusty proposes to Princess Penelope and the boys (Bart and Milhouse) concoct a plan to stop the wedding. Bart interrupts the ceremony and starts to show Penelope evidence of all of Krusty's past 15 wives. However, Penelope loves him so much she wants to continue with the wedding anyway. Seeing this, Krusty realizes that he isn't good enough for Penelope and tells her that he plans to leave her at the altar. A heartbroken Penelope goes to Paris where Krusty later joins her where they seemingly are going to live happily ever after.
To Read More here.